An X-ray computed tomography apparatus is provided with a gantry and a bed. In the state where a top plate is slid in the bore of the gantry, a CT scan is performed such that a to-be-imaged portion of a subject lying on the top plate can be included in the imaging range.
The bed supports the top plate at one end in the slice direction. With this structure, the front portion of the top plate tends to sag in accordance with an increase in the amount by which the top plate is slid into the bore of the gantry. If the top plate sags as above, the subject may be shown at a displaced position in a reconstructed image, resulting in a wrong diagnosis being made.